One of the main problems in digital wireless communication system is the dispersive fading cause by multi-path propagation in transmission channels. Therefore high performance adaptive equalizers play a very important role in modern digital wireless communication systems to combat multi-path fading. Inter symbol interference is one effect of multi-path fading.
In a digital modem, the gain control signal can be derived directly from the received I F signal. This approach however lacks precision, especially in a selective fading environment. To improve the accuracy, Automatic Gain Control circuits are built based on decision-directed algorithms. Thus in order to have a valid and stable control for the Automatic Gain Control AGC circuit, it is required to wait for the synchronization loops (carrier/clock) and also the equalizer to stabilize. This process takes several symbol intervals before all the loops converge and increases the re-synch time.
Standard implementations of Adaptive Time Domain Equalization (ATDE), requires in order to eliminate inter symbol interference (ISI) only to adjust the side coefficients of the ATDE relative to the center tap coefficients. The center coefficients for the through- and cross-sections of the ATDE are normally set to 1 and 0, respectively. These coefficients are fixed and are not dynamic.
By using the present invention, an intermediate frequency (IF) automatic gain control can be used alone with the incorporated AGC in the ATDE circuit. This implementation has the advantage of reducing the re-synch time for the modem as well as capability of correcting I/Q amplitude and phase imbalance.